This invention relates to valves, particularly those valves employed in fuel injection systems for internal combustion engines. More particularly, the valves of the invention use the change in dimensions of a piezoelectric element to effect movement of a valve needle from a closed position to an open position.
It is known that upon application of an electrical field across piezoelectric materials they expand or contract along known axes, depending on the direction in which the electrical field is applied. It is further known to stack a number of piezoelectric elements so that their cumulative expansion or contraction effect provides an increased mechanical movement. It is also known that piezoelectric elements having these expanding and contracting properties can be used to pump fuel from an injector by alternating an imposed electric field at suitable intervals. For example, Benson in U.S. Pat. No. 3,391,680 describes such a pump where the piezoelectric element is used to pressurize the fuel.
The present invention does not relate to a piezoelectric actuated pump wherein the piezoelectric element pressurizes and pumps the fuel but rather relates to a valve for precise metering and control of small quantities of an already pressurized fluid. In conventional fuel injection systems, high pressure, timed metering pump systems are used with relatively inexact timing and with nonuniform injected amounts of fuel. These are especially unsuitable for diesel engines and result in incomplete combustion which in turn increases adverse effects including both air and noise pollution.